The present invention relates to an impact serial printer of small size and having a relatively large number of type elements.
Recently, there has been remarkable progress in the development of personal type printers and printers suitable for use in hand held devices, particularly in the use of small-sized and light-weight printers in desk-top calculators and the like. As the printer incorporated in such calculators, so-called impact type serial printer are most welcomed partly because it can provide a clean printing of data and partly because it is suitable for a printing on ordinary paper.
This type of printer, although the size is small and the construction is advantageously simple, is inferior to the conventional large-sized printer in that the number of type elements mounted on a type wheel is limited and this undesirably restricts the variety of characters that can be printed.
To overcome this problem, the present applicant has proposed in Japanese Patent Publication No. 9298/1980 corresponding to U.S. Pat. No. 4,051,942, a small-sized serial printer having two type wheels one of which being shiftable in the direction of the line to be printed while the other being held at the initial column position. In operation, the type elements of these type wheels are selectively struck to effect the printing. This serial printer can have a small size and be comparatively compact because only one type wheel is shiftable. However, if the overall size of the printer has to be maintained small, it becomes impossible to have a large diameter for the type wheel, so that the number of the type elements is naturally limited. In addition, it is difficult to make two-color printing.